Containers of the above-mentioned type and having increased capacities, vertically elongated and lightweight containers (e.g., polyethylene terephthalate (PET) bottles) have found wide use in recent years, so that when transported on belt conveyors or roller conveyors which are usually used, these containers are liable to tumble and transport is difficult. Conveyors further have the problems, for example, of necessitating accurate positioning, occupying a large space as fixed equipment and requiring a high equipment cost.
Container transport apparatus are therefore already in use which comprise two screws made of resin or the like and arranged in parallel at a specified distance from each other and which are adapted to transport containers by rotating the screws, with the neck of each container held between the screws (usually with a flange at the neck of the container in engagement with the screws to hold the container therebetween in suspension).
The apparatus transports containers by a principle entirely different from that of conventional conveyors, i.e., by the frictional contact of the screws with the neck of the container, and permits accurate container position, facilitated automation of production lines, a simple and compact construction and low equipment cost.
Generally, the screws for use in the apparatus comprise a rigid rod prepared from resin or the like by solidification and are formed with a helical continuous groove. However, due to their rigidness, such screws cannot be employed for curved paths of transport, although they are usable for straight transport paths. Accordingly, the curved transport path requires another transport device, which renders the overall container transport apparatus complex in construction and more costly as equipment and is likely to impede smooth transport.
On the other hand, coiled wires are available which are similar in construction to the screws described above. Wires of this type are conventionally used for transporting powder and granular materials, and many of them are made of a metal such as steel. Apparatus for transporting powder and granular materials comprise such a coiled wire inserted in and extending through a metal or resin pipe, and are so adapted that the powder and granular materials placed into an inlet formed in one end of the pipe are transported to an outlet formed in the other end thereof by rotating the wire.
However, since the wire is made of a metal material, the pipe undergoes marked abrasion. Especially when the apparatus is initiated into operation, the wire is very likely to come into contact with the pipe inner wall, which in turn is ground by the wire and easily wears away. It is therefore important to avoid the abrasion of the pipe inner wall to the greatest possible extent to reduce the cost of maintenance.
Accordingly, an object of the present invention is to provide a screw most suited for use in apparatus for transporting powder and granular materials as well as in container transport apparatus to thereby overcome the foregoing problems.
Another object of the present invention is to provide a novel apparatus for transporting containers or powder and granular materials with use of the screw fulfilling the above object.